The output voltage generated by an amplifier of this type is substantially sinusoidal, except for the flattened peaks of its half-cycles resulting from the clipping effect due to saturation of the output transistors. The symmetry of the wave flanks, however, is disturbed specifically by the aforementioned second transistor to which the oscillations to be amplified are applied. As the first transistor overdrives the second transistor, the virtual capacitance at the input of the second transistor controlled thereby (formed between the base and the emitter of the latter transistor) is partly discharged so that a certain charging current must flow into that input capacitance at the end of the saturation interval before this second transistor will again conduct. This delays the desaturation of the one output transistor referred to above, whose operation is in phase with that of the first transistor in the input stage, leading to a distortion of the wave shape of the amplified output signal.
Such a distortion is particularly unwelcome when the cascaded output transistors are connected across an unbalanced d-c power supply; in that case, the harmonics generated by the distorted signal peak may strongly interfere with nearby electronic equipment, aside from entailing a substantial loss of power.
Since the delay in the recharging of the virtual input capacitance of the controlled transistor is determined by the circuit parameters and is practically independent of frequency, the resulting distortion becomes more significant at the higher frequencies of the operating range.